Mold core



June 15, 1965 J. w B 3,188,705

MOLD CORE Original Filed Dec. 29, 1958 INVENTOR. 6j BY fiaacfwddyze IATTORNEY United States Patent 3,188,7d Patented June 15, 1965 OfiliceThis invention relates to an expansion joint for a member of a thermaldevice having a limited surface portion thereon subjected to rapid andextreme cyclic changes of surface temperature and a method of formingsame.

'More particularly, the invention pertains to a method of makingarticles which have surfaces that are subject to severe cyclic thermalexpansive and contractive conditions relative to the other surface andinterior portions of the article, such as in internal combustion enginesand the like.

The present patent application is a division of my copending UnitedStates patent application Serial No. 783,-

. 370, which was filed on December 29, 1958, and is owned by theassignee of the instant patent aplication.

The various surfaces defining a combustion chamber or cylinder of aninternal combustion engine are subjected to rather severe cyclic thermalconditions due to the extremely rapid changes in temperature alternatelyimposed on these surfaces by the heats of compression and combustion andby the flow of relatively cool, gaseous charges into the cylindersduring the engine operating cycle.

These changes in surface temperature result in the cyclic composition ofexpansive, compressive and contractive, tensivc stresses on thesesurfaces and the immediately adjacent layers of the variouscylinder-defining members. In time these cyclic stresses result infatigue cracking of these surfaces. Such cracking generally occursintermediate and adjacent ports or openings in such members Where thesurface layer subjected to such cyclic stressing is of reduceddimension. Such cracking is also particularly prevalent in thoseapplications where the engine is subjected to excessive fluctuations inload and speed; factors which result in sudden applications ofrelatively cool, incoming air onto overheated cylinder-definingsurfaces.

This invention contemplates providing the combustion chamber surfaces ofa thermal device of the type described with expansion joints similar infunction to those shown and described in United States patentapplication Serial No. 650,249, now United States Patent No. 2,893,-371, filed April 2, 1957, in the name of Vernon E. Schafer, In, entitledExpansion Joint and which is assigned to the assignee of the presentinvention. Such expansion joints are formed by casting metal insertswhich are coated with a fusion-inhibiting material into thecylinderdefining members adjacent critical areas. These insertsintersect the combustion chamber surface and extend through the layer ofthe member normally subjected to such cyclic expansive and contractivethermal conditions. Under engine operating conditions, the initialexpansive compression imposed on this surface layer stresses this layerbeyond its compressive yield point for the temperatures involved andaffects the formation of grooves immediately adjacent to and includingthe opposite sides of the insert. These grooves serve to accommodate andisolate subsequent expansion and contraction of the surface layer fromthe adjacent critical areas.

In casting steel inserts in a cast iron engine cylinder head for theabove purpose, the carbon in the molten cast iron has a tendency todiffuse into the metal of the insert on contact. This diffusion ofcarbon changes the characteristics of the steel whereupon the insert hasa tendency to melt and fuse with the cast iron, destroying the intendedbeneficial effects of individuality.

Accordingly, it is a primary object of my invention to provide a rapidand economical means to prevent this diffusion and to provide a methodof economically casting a steel insert in a cast iron cylinder head soas to retain individuality of the insert.

Other objects, features and advantages of the present invention willbecome more apparent from the following description of preferredembodiments thereof and from the drawing, in which:

FIGURE 1 is a fragmentary sectional view of the exhaust port area in thecylinder head of an internal combustion engine of the uniflow,two-cycle, diesel type;

FIGURE 2 is a perspective view of one form of insert shown in FIGURE 1;

FIGURE 3 is a perspective view of a second form of insert, such as shownin FIGURE 1;

FIGURE 3a is an enlarged fragmentary sectional view of FIGURE 3; and

FIGURE 4 is a perspective view of a modified form of insert adapted foruse in place of the insert shown in FIGURE 3.

Referring more particularly to the drawing, FIGURE 1 shows a portion ofa cylinder head 19 of a uniflow, twocycle, diesel engine. Each cylinderin the engine is provided with two exhaust passages 12 which arerespectively connected to exhaust ports 14 which flank an opening (notshown) provided in the head for the nozzle of a fuel injector. The outerperiphery 16 of the exhaust ports 14 is beveled to seat the heads of twoexhaust valves (not shown) which are reciprocably mounted in the head.

As indicated above, the combustion chamber or fire deck surface 18 ofthe cylinder head of such an engine is particularly susceptible tosurface cracking intermediate and adjacent the valve ports and injectornozzle opening. The cracking which occurs intermediate the injectoropening and the exhaust ports is generally in a diametrical plane commonto the several openings. The expansion and contraction of the fire decksurface parallel to this common diametrical plane also tends to developsunbursttype cracking of the fire deck surface radially outwardly fromthe exhaust ports transversely of this common diametrical plane.

As shown in FIGURE 1, inserts 2t) and 22 are cast into the cylinder headin accordance with the invention and serve to isolate the cyclicexpansion and contraction of the combustion chamber surface from thecritical areas intermediate and adjacent to the injector opening, thevalve ports and other openings through the fire deck of the cylinderhead. These inserts are of limited mass to prevent chilling duringcasting and, as shown in FIGURE 3a, have a coating 23 to prevent fusionof the insert with the molten metal during the casting process.

In the illustrative embodiments these inserts are first stamped into thestructures shown from rolled sheet steel, are then coated, and cast inthe cylinder head as hereinafter described. In the illustrativeembodiments, the inserts 2 and 22 are arranged in pairs in parallelspaced relation flanking the critical areas intermediate the valve portopenings 14, thereby serving to isolate the cyclic expansion andcontraction of the remainder of the combustion chamber surface fromthese critical areas. The inserts 20 and 22 each have corrugatedportions 24 and .26, respectively, normal to and intersecting thesurface faces of the cylinder head. By using such corrugations,

it hasbeen found that such inserts can be us'edwithout increasing thethickness of thefiredeck inasmuch as the V interlocking,'serratedsurfaces carry/the compression and combustion loads imposed on theadjacent portions of the fire deck. i

I The inserts 20 and 22 are'terminated inwardly of the fire deckfromtheir corrugatedportionsby rounded or cylindrically looped portions '28.These loopedportions are open lengthwise to permit the free flow ofmolten metal within the loop during the casting process and serve toterminate the cracks formed in the head by the use of such inserts. Theinserts'22 each havea single looped portion 28 which extends inparallelspaced relation to the combustion chamber surface and intersectsthe counterbores for the valve seat inserts at its opposite end. Theinserts -20 are each rounded to provide two cylindrical or loopedportions 28 and '30 formed at right angles to each other. The loopedportion 30 is'normalto and intersects the combustion chamber surface/atone end, and the looped portion 28 extends in; parallel spaced: relationto the combustion chamber surface. and intersects the ading thicknessesof approximately 0.0005 inch to 0.0015 inch can be used for mostapplications without impairing surface detail.

After the coating is applied it is dried so that the insert can bereadily handled prior to the casting operation without detrimentallyaffecting the coating, such as by scratching, nicking, etc. Although thecoating can be dried at room temperature, it is preferred to acceleratethe drying by heating at elevated temperatures. When using a suitablesilicone resin ori'tributyltitanate as the carrier, the coating ispreferably dried at temperatures from about 200- F. to SOOF. for about10 tominutes.

llhave found that successfulresults are obtained when using amixture]containingapproximately 20% to 40%, by Weight,aluminum oraluminum base alloys and levia gated alumina in amounts fromapproximately 5% to 10%, by weight. In some instances, amounts ofalumina jacent valve port 14 at-its end opposite the looped portion 30.r V v v Under normal engine operating conditions, the cyclic expansionof the surface layer of the head adjacent the combustion chamber affectsthe formation of narrow M grooves (not shown) and in, the surface of thecasting im mediately adjacent the inserts '20 and :22, respectively.Since the compressive stresses resulting from such cyclic expansionexceed the .yield points of the insert, and head materials at thetemperatures involved, :these grooves are formed in part by the outwardextrusion of a portion of the insert and in part by the permanentupsetting of the adjacent surface layer. The grooves are thus formedduring'the initial or breaking-in period. of engineoperation to thedepth of this surface layer subjected to cyclic thermal conditions andareadapted to accommodate subsequent expansive and contractive plasticflow of this surface layer -without imposing further compressive andtensive stresses on the critical areas of the head intermediate theinserts.

A third form of insert 32 is shown in FIGURE 4.' This insert isgenerally triangular in shape and particularly designed for useinapplications similar to that for which the inserts 20 and 22 are used inthe above-described embodiment. As shown, the insert 32 has a portion 34corresponding to the portion 24 of insert 20 and having corrugationsintended to provide interlocking surfaces parallel to the combustionchamber surface of thefire deck. A rounded bead 36 is formed :arrcuatelyand generally diagonally of the corrugations and is adapted to terminate the insert created crack; intersecting the exhaust port 14 at oneend and the surface 18 of the combustion chamber at its other end. V

In accordance with my invention, the formed insert is coated with amixture of powdered aluminum or a pow dered aluminum base alloy,levigated, or powdered, alumina and a carrier, which preferablyfunctions as a binder. A sufficient quantity of the coating mixture isapplied to form a coating having a thicknessv of at least 0.0005 inchby. spraying, dipping, rolling, brushing or the like. The maximumthickness of ,a coating which can be used is dependent upontheparticular .applicationand, in general, a variety of coating thicknessesabove vabout 0.0005 inch can be used. The thickness of the coating ashigh as approximately 20%, by weight, are preferred. In'referring toaluminum base alloys, I intend to encompass alloys containing at leastabout 80% aluminum.

The particle size of the aluminum or aluminum base alloys, as wellas thealuminaare preferably of such a size that they can be readily dispersedin a suitable carrier and do not readily settle out. Generallly, Iprefer to use particle sizes of at least about 2 microns since particlesof smaller size tend to form aggregates which are not readily brokenduring the mixing, thus inhibiting dispersion of the individualparticles 'in the carrier.

Generally, aluminum or alurninum base alloys which have a particle sizethat will pass through a standard 400 diameter of about '2 microns canbe'used. Particle sizes I of the aluminum or aluminum base alloys inexcess of about 400 mesh tend to be exceedingly inefficient inmaintaining separation of the aluminum particles and are quite difiicultto maintain in uniform dispersion. Such particles tend to settle outquite rapidly from the mixture.

, Since the aluminavis quiteimportantin preventing the wetting of thesurface of the insert by the molten casting metal, it is important thatthe size of the alumina particles be maintained fairly small. Ihavefound that levi gated alumina having particle sizes of approximately2 microns to 10 microns provide generally satisfactory results.. 1

The carrier for the alumina and aluminum base alloys or aluminum whichis to be used can be any type which will function satisfactorily in thegiven'application. The

carrier preferably acts as a binder for the, particles, mak ing themadhere to the surface of the insert. In some instances, the carrier canbe composed of a binder. plus a volatile solvent which is used to thinthe -mixture. Although 'a binder is generally preferredfor the-carrier,in some instances the carrier can be only a volatile solvent.

However, in instances where the inserts must be handled to some extentbefore the casting operation and in which handling the parts may besubjected to some abuse,

. it is essentially desirable that the aluminum and aluminum generallyis limited only by that thickness which will'tend,

7 since mixtureof such a thinner with to decompose the tributyltitanate.

oxide be supported in a carrier which has bonding or adhesivecharacteristics. jEspecially satisfactory results have been obtainedusing tributyltitana-te and polyorganosiloxanes as carriers which havebonding characteristics. Alkyl-aryl and dialkyl polyorganosiloxanes,such as a phenyl methyl polysiloxane or a dimethyl polysiloxane, eachhaving a molecular Weight in the nature of about 1400 to 1600, isgenerally useful.

Volatile solvents, such as acetone, alcohol, methyl ethyl ketone, can beused to thin the mixture so that it can behandled more readily. Whenusing tributyltitanate as a binder, however, extreme care must beemployed to avoid using a thinner which has excessive moisture thereintributyltitanate tends As a specific example of my invention inserts,such as hereinbefore' described, made of SAE 1008 steel can be cast in auniflow, two-cycle,,diesel engine cylinder head having a compositionwhich is as follows, all percentages An insert of SAE 1008 steel whichis placed in contact With a molten cast iron alloy, such as describedabove,

readily absorbs carbon from the molten alloy. The melting point of thesteel is reduced to such an extent that the steel insert is melted andblends with the cast iron, destroying the individuality of the insertnecessary to obtain the benefits of the invention.

However, I have found that such action was eliminated by dipping theinsert into a liquid mixture containing 25 milliliters oftributyltitanate, 15 grams aluminum powder and 3 grams levigatedalumina. After dipping the part I in the mixture, the part was shakenvigorously to remove excessive amounts of the coating mixture andsubsequently dried for 15 minutes at approximately 300 F. The part wassubsequently located in a cylinder head mold in spaced relationship toform the cylinder head previously described. Generally, any type of moldcan be used which is suitable for the casting of cylinder heads withoutinserts. The inserts are maintained in position in the mold in thenormal and accepted manner for casting inserts. Typically, the moldcavity surface can be grooved and the inserts placed therein. With theinserts in the mold, the molten cast iron is introduced to form thecylinder head.

After the casting operation, the mold members were removed in aconventional manner leaving the resultant head casting accessible forfurther treatment. The casting was then cleaned and subsequentlymachined in the usual manner in the finished fire deck surface and valveports, as shown in FIGURE 1. These machining operations, of course,insure that the inserts properly intersect the finished surfaces of thehead.

In some instances this invention is preferred for casting other types ofsteel inserts in cast iron articles. This invention has been especiallysatisfactory in forming cast iron castings which have exceedinglycomplex passages therein. Finished castings of this type are frequentlynot easily made using conventional coring techniques. In such instances,it may be desirable to coat, in a manner such as herein described, theexterior of a tubular member which is preformed to the desired contourof the passage in the casting. The coated, preformed tubing is thensuitably located in a mold and the molten casting metal introduced. Inthis manner highly satisfactory results are obtained which cannot bereadily obtained by conventional coring methods.

It is also contemplated that, in some instances, the subject mixture isespecially satisfactory when used as a core wash in the known andaccepted manner. Under some circumstances it is desirable to coat themold cavity-defining surface of a chill in a mold. In such event thesubject type mixture provides an especially satisfactory coating whichinhibits wetting of the chill and diffusion across the interface betweenthe chill and the molten casting metal.

Although this invention has been described in connection with certainspecific examples thereof, no limitation is intended thereby except asdefined in the appended claims.

I claim:

1. in a mold, a mold core located in a mold cavity, a coating on saidmold core of a mixture comprising, by weight, approximately about 20% to40% of a powdered metal from the group consisting of aluminum andaluminum base alloys, about 5% to 20% powdered alumina and about 40% toof a binder.

2. In a mold, a mold core located in a mold cavity, a coating on saidmold core of a mixture comprising, by weight, approximately about 20% to40% of a powdered metal having a particle size of from about 400 mesh toabout 2 microns from the group consisting of aluminum and aluminum basealloys, about 5% to 20% powdered alumina and about 40% to 75% oftributyltitanate, said coating having a thickness of at least 0.0005inch.

3. In a mold, a mold core located in a mold cavity, a coating on saidmold core of a mixture comprising, by weight, approximately about 20% to40% of a powdered metal selected from the group consisting of aluminumand aluminum base alloys, about 5% to 20% powdered alumina and about 40%to 75 of a binder selected from the group consisting of phenyl methylpolysiloxane, dimethyl siloxane and tributyltitanate.

References Cited by the Examiner UNITED STATES PATENTS 2,507,068 5/50Underwood 1175.3 2,599,185 6/52 Lepp et al 10665 2,872,715 2/59 Bean22202 2,875,485 3/59 Schneider 22-493 2,903,375 9/59 Peras 1l7-5.32,975,494 3/61 Cooper 22l93 FOREIGN PATENTS 584,160 1/47 Great Britain.

MICHAEL V. BRINDISI, Primary Examiner.

MARCUS U. LYONS, Examiner.

1. IN A MOLD, A MOLD CORE LOCATED IN A MOLD CAVITY, A COATING ON SAIDMOLD CORE OF A MIXTURE COMPRISING, BY WEIGHT, APPROXIMATELY ABOUT 20% TO40% OF A POWDERED METAL FROM THE GROUP CONSISTING OF ALUMINUM ANDALUMINUM BASE ALLOYS, ABOUT 5% TO 20% POWDERED ALUMINA AND ABOUT 40% TO75% OF A BINDER.